The electrochemical cell described by the balanced chemical reaction has a standard emf (electromotive force) of 0.27 V. Calculate the equilibrium constant (Kc) for the reaction at 298 K. Round your answer to 3 significant figures.

H2O2(aq) + 2ClO2(g) → O2(g) + 2HClO2(aq)

i always do this problem wrong because i can never find the right n
and you use -RTlnK=-nFE0cell right?